In quantum circuits, a Josephson ring modulator is coupled to two superconducting microwave resonators and three-way mixing is performed between differential modes supported by the two superconducting microwave resonators and a non-resonant, common drive fed to the Josephson ring modulator. Due to coupling the Josephson ring modulator to the two superconducting microwave resonators, the device is limited in the choice of the frequency of differential modes, which can cause one or more problems. For example, coupling the Josephson ring modulator to low-frequency, transmission-line resonators can have various problems, such as occupying a large area (e.g., a large footprint). Another problem is the relatively large linear inductance associated with the low resonance-frequency transmission-line compared to the inductance of the Josephson ring modulator. This can result in a very reduced participation ratio which in turn requires, for its operation, very high external quality factors (Qs) for the resonators. However, high external Qs for the resonators is undesirable because it can give rise to very narrow dynamical bandwidths, which severely limit the device usability and practicality.
In addition, coupling the Josephson ring modulator to low-frequency, lumped-element resonators can require the use of large lumped capacitances and large lumped inductances. Large lumped capacitances and inductances are difficult to realize in practice. Large capacitances can have considerable loss (lowering the internal Q of the device) and as a result can cause a considerable portion of the quantum signal to be lost. Large geometric inductances usually suffer from parasitic capacitances which limit their utility. Large kinetic inductances usually rely on unconventional thin superconductors which are difficult to fabricate and integrate.